Wireless communication system with high efficiency/high power optical source

ABSTRACT

An optical communication system is provided which includes an optical signal transmitter which communicates high bandwidth, high power frequencies. The optical signal transmitter includes a high efficiency/high power optical source such as an optical magnetron or a phased array source of electromagnetic radiation, and a modulator element. The modulator element may be within a resonance cavity of the high efficiency/high power optical source (intra cavity) or external to the cavity (extra cavity). The modulator element serves to modulate output radiation of the high efficiency/high power optical source to produce a modulated high frequency optical signal which may be transmitted through the air. The optical signal transmitter is particularly useful in providing the last mile connection between cable service operators and end users.

RELATED APPLICATION DATA

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/798,623, filed Mar. 1, 2001, which is a continuation-in-partof U.S. patent application Ser. No. 09/584,887, now U.S. Pat. No.6,373,194, filed Jun. 1, 2000, U.S. patent application Ser. No.10/050,744, filed Jan. 16, 2002, which is a divisional of U.S. patentapplication Ser. No. 09/584,887, and U.S. patent application Ser. No.09/995,361, filed Nov. 27, 2001, all of which are hereby incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to wireless communicationsystems for communicating information, for example, video and voicedata, and more particularly to a wireless optical communication systemwith a high efficiency/high power optical source.

BACKGROUND OF THE INVENTION

The need for network architectures that provide broad frequencybandwidth is evident from the increased user demand for programs,products and services such as high speed Internet access,voice-over-Internet protocol (VoIP), video-on-demand (VOD), interactivetelevision, digital HDTV, and broadband telephony services such asvideophone, videoconferencing, etc. Improvements to meet this need mustdeliver hundreds of Megabits per second, in send and receive modes, andpreferably in duplex, i.e., simultaneously sending and receiving.

Cable companies, telecommunications companies, satellite and wirelessproviders, and other service providers have developed a number ofmethods to increase frequency bandwidth. For example, newercommunication lines being built today are based on fiber optictechnologies which are capable of transmitting large volumes ofinformation at very high speeds (high-bit-rate data transmission). Mostcities are linked by communication lines capable of carrying informationsuch as video and voice data, requiring a high frequency bandwidth.

Little or no feasible technology presently exists, however, to deliverhigh frequency bandwidth, and in particular two-way bandwidth, at theuser terminal end of existing communication networks. One reason forthis is that the commonly referred to “last mile” local drop to the enduser is typically still the legacy copper line installed decades ago fortelephone service. Because the legacy copper lines were designed forperformance that did not contemplate today's fiber optic capabilities,the end users with copper lines cannot avail themselves of the high bitrates that a modern long haul infrastructure can provide. Quite simply,the legacy links as well as the architecture of the central office(telephone exchange) cannot deliver the information transfer capabilitydesired for all the data, video, etc. The end user has thus been limitedby his or her local drop (or “last-mile”) connection to the serviceprovider.

Fiber optic cable lines and satellites may provide suitable transmissionof high frequency communication signals, but these methods are notwithout drawbacks. For instance, laying cable lines to every end user iscost prohibitive, especially in an urban environment. Satellites,although capable of transmitting high frequency data, are limited due toboth spectrum allocations and to a limited number of orbital slots; thatis, there is insufficient capacity to deliver high bandwidth service tomillions of users. Moreover, the complexities involved with highfrequency two-way satellite bandwidth (duplex mode) render it toodifficult and expensive to implement.

Short-wavelength optical systems also have been proposed, claimingoptical data transmission with high bandwidth. Short-wavelength opticalsystems at near and visible frequencies, however, suffer from theinability to penetrate inclement weather such as clouds and rain.

In view of the aforementioned shortcomings associated with presentcommunication and information networks, there exists a strong need for acommunication system and method that can transmit and receiveinformation with respect to the last-mile using a high frequencybroadband carrier.

SUMMARY OF THE INVENTION

The present invention provides an optical communication system with anoptical signal transmitter at the last mile for transmitting informationat increased frequency bandwidths. The optical signal transmitterincludes a high efficiency/high power optical source which operates athigh efficiency, high power optical frequencies such as the infrared andvisible light bands, and which may extend beyond into higher frequencybands such as ultraviolet, x-ray, etc. As a result, the communicationsystem of the present invention may be used to solve the last mileproblem exhibited in most existing communication networks. Moreover, theoptical communication system is advantageous over conventionalshort-wavelength optical systems at near infrared and visiblefrequencies in its ability to penetrate clouds and rain.

According to one particular aspect of the invention, there is providedan optical communication system, including an optical signalcommunication station for communicating optical signals to an end userspaced from the optical signal communication station. The optical signalcommunication station includes a high efficiency/high power opticalsource which transmits high frequency optical communication through theair to the end user.

According to another aspect of the invention, there is provided a methodof communicating high frequency optical signals through the air from anoptical signal communication station to an end user. The method includesmodulating an information signal with a high efficiency/high poweroptical source to obtain a high frequency optical signal, andtransmitting the high frequency optical signal through the air to theend user.

According to another aspect of the invention, there is provided anoptical communication system, including a service provider, and opticalfiber network, and a high efficiency/high power optical source. Theservice provider receives information signals and converts theinformation signals into optical signals having a frequency in the broadbandwidth frequency range. The optical fiber network receives theoptical signals from the service provider. The high efficiency/highpower optical source receives the optical signals from the optical fibernetwork and transmits the optical signals through the air to an end userspaced from the high efficiency/high power optical source.

According to another aspect of the invention, there is provided anoptical communication system, including an optical signal communicationstation which communicates through the air to one or more end users. Theoptical signal communication station includes a first optical signalreceiver and a first high efficiency/high power optical source. The enduser(s) are spaced from the optical signal communication station, andeach end user includes a second optical signal receiver and a secondhigh efficiency/high power optical source. The first highefficiency/high power optical source transmits through the air firstoptical signals having a frequency in the broad bandwidth frequencyrange, and the second optical signal receivers of the respective endusers detects the first optical signals. The second high efficiency/highpower optical source transmits through the air second optical signalshaving a frequency in the broad bandwidth frequency range, and the firstoptical signal receiver of the optical signal communication stationdetects the second optical signals.

According to yet another aspect of the invention, there is provided anoptical signal transmitter including a high efficiency/high poweroptical source and a modulator element. The high efficiency/high poweroptical source includes an anode, a cathode and an optical resonator.The anode, cathode and optical resonator are coaxially aligned and theanode and optical resonator are separated by a resonant cavity. Themodulator element is disposed within the resonant cavity for modulatinga high frequency optical signal of the high efficiency/high poweroptical source.

According to another aspect of the invention, there is provided anoptical signal transmitter, including a high efficiency/high poweroptical source, a plurality of output waveguides and respective outputantennas, and a plurality of high frequency modulator elements. The highefficiency/high power optical source produces high frequency opticalsignals, and includes an optical resonator having a plurality ofradially extending output ports through which the optical signals aretransmitted. The plurality of output waveguides and respective outputantennas are connected to and extend radially outwardly from the opticalresonator at the respective output ports. Each of the plurality of highfrequency modulator elements modulates the high frequency optical signalwith an information signal to produce a modulated high frequency opticalsignal and directs the modulated optical signals toward a plurality ofrespective directions.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrativeembodiments of the invention. These embodiments are indicative, however,of but a few of the various ways in which the principles of theinvention may be employed. Other objects, advantages and novel featuresof the invention will become apparent from the following detaileddescription of the invention when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an environmental view illustrating an optical communicationsystem in accordance with the present invention.

FIG. 2 is an environmental view illustrating in greater detail aneighborhood communication node and a neighborhood end user of theoptical communication system of FIG. 1.

FIG. 3 is a cross-sectional top view of an optical signal transmitter inaccordance with one embodiment of the present invention.

FIG. 4 is a cross-sectional view of the optical signal transmitter ofFIG. 3 as viewed from line 4-4 in FIG. 3.

FIG. 5 is a cross-sectional side view of a phaser for use in the opticalsignal transmitter of FIG. 3.

FIG. 6 is a cross-sectional top view of the phaser of FIG. 5 as viewedfrom line 6-6 in FIG. 5.

FIG. 7 is a cross-sectional top view of an optical signal transmitter inaccordance with another embodiment of the present invention, including amixer element.

FIG. 8 is a cross-sectional top view of an optical signal transmitter inaccordance with another embodiment of the present invention.

FIG. 9 is a cross-sectional view of the optical signal transmitter ofFIG. 8 as viewed from line 9-9 in FIG. 8.

FIG. 10 is a cross-sectional top view of an optical signal transmitterin accordance with another embodiment of the present invention,including a mixer element.

FIG. 11 is a cross-sectional top view of an optical signal transmitterin accordance with another embodiment of the present invention,including a mode locking device.

FIG. 12 a is a cross-sectional top view of an optical signal receiver inaccordance with the present invention.

FIG. 12 b is a cross-sectional top view of an optical signal receiver inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to thedrawings, in which like reference numerals are used to refer to likeelements throughout.

Referring now in detail to the drawings and initially to FIGS. 1 and 2,there is illustrated an optical communication system 10 in accordancewith the present invention. The optical communication system 10 includesa broadband data source 12 such as a satellite, an intercity opticalfiber trunk line, or the like. The data source 12 provides broadbanddata such as multichannel video programming, on-demand programming,broadband telecommunications, etc. The optical communication system 10further includes a service provider 16 such as a cable service provider.The service provider 16 receives data from the data source 12 andprovides such data to a network of optical signal communication stations20, only one of which is shown in FIG. 1. The optical communicationstations 20 serve to communicate information from the service provider16 along the “last mile” to several associated neighborhood end users22.

In accordance with the present invention, and as is described in greaterdetail below, the optical signal communication stations 20 and thecorresponding neighborhood end users 22 are able to communicate atfrequencies which exceed 100 Gigahertz. Information may thus becommunicated through the air between the optical signal communicationstations 20 and the neighborhood end users 22 at hundreds of Megabitsper second in send and receive modes to enable, for example,video-on-demand (VOD), interactive television, and digital HDTV. Thoseof ordinary skill in the art will appreciate that the opticalcommunication system 10 in accordance with the present invention may beused to solve the problem experienced by previously known communicationsystems insofar as the inability to efficiently deliver informationrequiring a high frequency bandwidth to a user terminal end of acommunication network. The present invention efficiently solves suchproblem by enabling wireless communication of broad bandwidthcommunications to the neighborhood end users 22. The neighborhood endusers 22 may be individual homes, an apartment unit or complex,condominiums, private business, etc., as will be appreciated.

In the exemplary embodiment, the broadband data source 12 is a satellitewhich transmits video and audio information, for example, such as cabletelevision program services to the cable service provider 16. The cableservice provider 16, in turn, frequency multiplexes the transmittedsignal into a combined spectrum signal having a predetermined frequencydistribution and then converts the combined spectrum signal into abroadband optical signal, for example. The cable service provider 16transmits the broadband optical signal to the optical signalcommunication station 20 via an optical fiber network 26, such as aneighborhood trunk line as will be appreciated.

The illustrated optical signal communication station 20 includes a towerupon which an optical signal transmitter 28 is mounted. The opticalsignal transmitter 28 transmits the optical signal through the air toeach neighborhood end user 22 in a corresponding cell or zone. Eachneighborhood end user 22, in turn, includes an individual optical signalreceiver 34 for receiving the optical signal. One or more demodulators(not shown) serve to demodulate the modulated high frequency opticalsignals transmitted by the optical signal transmitter 28 in order toreproduce the information signal, as will be appreciated by those ofordinary skill in the art.

Each neighborhood end user 22 optionally may include an optical signaltransmitter 36, which transmits through the air an optical signalincluding data or other information to the optical signal communicationstation 20. In such case, the optical signal communication station 20includes an optical signal receiver 38, which receives the opticalsignal from each end user 22 in the corresponding cell or zone. One ormore demodulators (not shown) included in the optical signal receiver 38serve to demodulate the modulated high frequency optical signalstransmitted by the optical signal transmitter 36 in order to reproducethe information signal, as will be appreciated by those of ordinaryskill in the art.

The optical signal transmitters 28 and 36 of the respective opticalsignal communication station 20 and the neighborhood end users 22 serveas high-efficiency sources of optical radiation which communicateinformation optically from the optical signal communication station 20to the neighborhood end users 22 and vice versa.

As is shown in FIG. 2, the optical signal communication station 20 alsoincludes a neighborhood communication node 40 which processes incomingand outgoing optical signals. The neighborhood communication node 40 iscoupled to the optical fiber network 26 through an optical fiberinterface 42. Optical signals incoming from the optical fiber network 26are routed by a signal switching and routing device 44 to an outgoingmultiplexer 46, which multiplexes the optical signal with respect to theneighborhood end users 22 before or as the optical signal is transmittedby the optical signal transmitter 28. Optical signals directed to thecable service provider 16, for example, optical signals carryinginformation requests for a particular program or service provided by theservice provider 16, are transmitted to and demultiplexed by an incomingdemultiplexer 48, before being routed by the signal switching androuting device 44 to the optical fiber network 26.

Turning now to FIGS. 3 and 4, a first embodiment of the optical signaltransmitter 28 is shown. In the illustrated embodiment, the opticalsignal transmitter 36 is substantially the same as the optical signaltransmitter 28, although the optical signal transmitter 36 typicallywill have only a single output. Therefore, the optical signaltransmitter 36 will not be described for sake of brevity. Those ofordinary skill in the art will appreciate that the optical signaltransmitter 28 alternatively may be of a different construction thanthat of the optical signal transmitter 36, and that the opticalcommunication system 10 may embody several different optical signaltransmitters depending on the frequencies and power requirements of theapplication involved.

The optical signal transmitter 28 includes a high efficiency/high poweroptical source such as the illustrated optical magnetron 52 whichoutputs high frequency optical radiation. A high speed modulator element56 is included within the optical magnetron 52 which modulates the highfrequency output radiation to produce a modulated high frequency opticalsignal. As is further described below, the optical magnetron 52 of theoptical signal transmitter 28 is capable of operating at frequencies onthe order of 100 GHz or more, enabling the optical signal transmitter 28to transmit high bandwidth optical signals along the last mile betweenthe optical signal transmitter 28 on the station 20 tower and theneighborhood end users 22.

The illustrated magnetron 52 includes a cylindrically shaped cathode 70with endcaps 71 at the respective ends of the cathode 70. The cathode 70is enclosed within a hollow-cylindrical shaped anode 72 which is alignedcoaxially with the cathode 70. The anode 72 has an inner radius which isgreater than the radius of the cathode 70 so as to define an interactionregion or anode-cathode space 74 between an outer surface 78 of thecathode 70 and an inner surface 80 of the anode 72. Terminals 82 and 84respectively pass through an insulator 85 and are electrically connectedto the cathode 70 to supply power to heat the cathode 70 and also tosupply a negative (−) high voltage to the cathode 70. The anode 72 iselectrically connected to the positive (+) or ground terminal of a highvoltage supply (not shown) via terminal 86. A pair of magnets 88 and 90are located at the respective ends of the anode 72.

The inner surface 80 of the anode 72 includes a plurality of resonantcavities 92 distributed along the circumference within the anode 72,which are sized according to the desired operating frequency. Everyother resonant cavity 92 includes a coupling port 94 which serves tocouple energy from the respective resonant cavities 92 to a commonresonant cavity 96. The coupling ports 94 are formed by holes or slotsprovided through the wall of the anode 72.

The common resonant cavity 96 is formed around the outer circumferenceof the anode 72, and is defined by the outer surface 98 of the anode 72and a cavity defining wall 100 formed within a resonant cavity structure102 such as the illustrated optical resonator. As is shown in FIG. 4,the optical resonator 102 forms a cylindrical sleeve 103 which fitsaround the anode 72. The common resonant cavity 96 is positioned so asto be aligned with the coupling ports 94 from the respective resonantcavities 92. The common resonant cavity 96 serves to constrain theplurality of resonant cavities 92 to operate in a pi-mode oscillation.That is, each resonant cavity 92 is constrained to oscillate pi-radiansout of phase with the resonant cavities 92 immediately adjacent thereto.

During operation, a power supply (not shown) applies heater current toand from the cathode 70 via terminals 82 and 84. Simultaneously, poweris applied as a dc voltage to the cathode 70 and anode 72 via terminals84 and 86. The dc voltage produces a dc electric field E which extendsradially between the cathode 70 and anode 72 throughout theanode-cathode space 74. The magnets 88 and 90 provide a dc magneticfield B in an axial direction which is normal to the electric field Ethroughout the anode-cathode space 74. The crossed magnetic field B andelectric field E influence electrons emitted from the cathode 70 to movein curved paths through the anode-cathode space 74. With a sufficient dcmagnetic field B, the electrons will not arrive at the anode 72, butreturn instead to the cathode 70. As the electrons emitted from thecathode 70 follow the curved paths through the anode-cathode space 74and pass in close proximity to the openings of the resonant cavities 92,a resonant field is created within the resonant cavities 92. Morespecifically, the electrons emitted from the cathode 70 tend to form arotating electron cloud which passes in close proximity to the resonantcavities 92. The electron cloud excites electromagnetic fields in theresonant cavities 92 causing them to oscillate or “ring”. Thesepersistent oscillatory fields in turn accelerate or decelerate passingelectrons causing the electron cloud to bunch and form rotating spokesof charge.

The optical magnetron 52 is capable of operating at frequencies higherthan 100 Ghz and with efficiencies on the order of 85%. Consequently,the illustrated optical magnetron 52 is well suited for the opticalsignal transmitter 28 requiring a high efficiency, high power output.

Of course, other high efficiency/high power optical sources mayalternatively be employed in the optical signal transmitter 28 to obtainsimilar operating frequencies and efficiencies, and such alternativesare contemplated by the present invention. For example, FIGS. 5 and 6illustrate a phased array source of electromagnetic radiation (phaser)112 in accordance with the present invention. In the Figures, likecomponents are designated by like reference numerals. The phaser 112 hasa different optical resonator and anode structure than that of theoptical magnetron 52. The optical resonator 116, that is the resonantcavity structure, has a cavity defining wall 118 that is curved andforms a toroidal shaped common resonant cavity 120. As is described infurther detail below, the anode 126 includes a plurality ofinterdigitated electrodes which permit very fine electrode spacingindependent of the operating wavelength.

As is shown in FIGS. 5 and 6, the phaser 112 includes permanent magnets138 and 140 and a corresponding cylindrical pole piece 150 mountedconcentrically about the axis A on each of the magnets 138 and 140. Eachof the pole pieces 150 includes a smooth, highly electrically conductivecladding 152 made of silver or the like. The pole pieces 150 aregenerally symmetric and face each other as shown in FIGS. 5 and 6. Thewidth W of the pole pieces 150 and corresponding cladding 152 defines arelatively wide anode-cathode space 154 therebetween. Each pole piece150 includes a plurality of electrodes 166 equally spaced about thecircumference of a circle with a radius rcb (FIG. 6) from the axis A.The electrodes 166 have a length of ¼λ, where λ is the wavelength at thedesired operating frequency. The electrodes 166 from the upper polepiece 150 are interdigitated with the electrodes 166 of the lower polepiece 150 as shown in FIG. 5 such that a cylindrical “cage” is formedabout the cathode 170 in the anode-cathode space 154 defined between therespective pole pieces 150. The radial distance from the electrodes 166to the outer edge of the pole pieces 150 (inclusive of the cladding 152)is λ/2, and the spacing between the opposing faces 178 of the polepieces 150 is slightly greater than λ/4 (to avoid electrode contact withthe oppositely facing pole piece 150). As a result, the opposing faces178 of the pole pieces 150 form a waveguide or parallel platetransmission line having a length along the radial direction of λ/2which begins at the edge of the cylindrical cage formed by theelectrodes 166 and opens into the common resonant cavity 120.

The cathode 170 extends along the axis A (e.g., through the lower magnet140 and the pole piece 150) so as to be centered within the cage formedby the interdigital electrodes 166. Terminals 192 and 194 respectivelypass through an insulator 195 and are electrically connected to thecathode 170 to supply power to heat the cathode 170 and also to supply anegative (−) high voltage to the cathode 170. The respective pole pieces150 in this embodiment are electrically connected to the positive (+) orground terminal of a high voltage supply (not shown) via terminal 196.

During operation, standing-wave electromagnetic fields cause the face178 and electrodes 166 of the upper pole piece 150 to be chargednegatively while the face 178 and electrodes 166 of the lower pole piece150 are charged positively. The resultant alternating positively andnegatively charged interdigital electrodes 166 cause horizontal electricfields to exist in the gaps between the electrodes 166. As thestanding-wave field reverses in time during the cycle of oscillation,the face 178 and electrodes 166 of the upper pole piece 150 becomepositively charged while the face 178 and electrodes 166 of the lowerpole piece 150 become negatively charged. The horizontal electric fieldsbetween the electrodes 166 thus reverse in direction during each cycle.These horizontal electric fields thus become the pi-mode fields whichinteract with the rotating electron cloud within the anode-cathode spaceto produce oscillations within the phaser 112.

It is noted that the phaser 112 of FIGS. 5 and 6 may be utilized inplace of the optical magnetron of FIGS. 3 and 4 in each of the hereindescribed embodiments.

Further details of the illustrated optical magnetron 52 and phaser 112and other suitable high efficiency/high power optical sources for use inthe optical signal transmitter 28 may be found, for example, in U.S.patent application Ser. Nos. 10/050,744, 09/995,361, 09/798,623, and09/584,887 (now U.S. Pat. No. 6,373,194), and published PCT ApplicationNo. PCT/US01/16622, the subject matter of which is assigned to theassignee of the present invention, and which are hereby incorporatedherein by reference in their entirety.

Referring again to FIGS. 3 and 4, the high speed modulator element 56 isdisposed within the common resonant cavity 96 of the optical signaltransmitter 28. The illustrated modulator element 56 is made of asuitable layer of electro optic material such as lithium niobate and hasa hollow-cylindrical shaped structure which is aligned coaxially withthe cathode 70 and anode 72. The outer circumference 208 of themodulator element 56 abuts the cavity defining wall 100 formed withinthe optical resonator 102. The data input terminals 210 and 212 areelectrically connected to optically transparent electrodes (not shown)on opposite sides of the layer of electro optic material to supply adigital modulating signal to the modulator element 56.

During operation of the optical signal transmitter 28, a modulatingvoltage is applied to the data input terminals 210 and 212 of themodulating element 56 by the outgoing multiplexer 46. As a result ofsuch modulating voltage, the dielectric constant of the modulatingelement 56 changes, for example. The change in the dielectric constantcauses the optical magnetron 52 to shift its frequency, phase and/oramplitude, for example, thereby modulating the optical radiationtransmitted by the optical magnetron 52. For example, the optical signaltransmitter 28 in accordance with the present invention transmits dataat a rate of up to about 10 gigabits per second.

The modulated optical signals are transmitted through a plurality ofoutput ports 214. The output ports 214 are formed by holes or slotsprovided through the wall of the optical resonator 102. In theillustrated embodiment, the optical signal transmitter 28 includes aplurality of output waveguides 216 and respective output antennas 218(such as a horn antenna or other suitable antenna) suitably connected toand extending radially outwardly from the optical magnetron 52 at therespective output ports 214. The output waveguides 216 and output hornantennas 218 direct the output signals toward a plurality of selecteddirections, for example, an output directed to each of the plurality ofneighborhood end users 22. In the embodiment illustrated in FIGS. 3 and4, all of the output signals emitted from the horn antennas 218 carrythe same data stream. This data stream may be multiplexed (e.g.,time-division, frequency division, etc.) in order that each neighborhoodend user 22 receives select programming specific to the neighborhood enduser 22.

As will be appreciated by those of ordinary skill in the art, theoptical signal transmitter 28 may include any number of outputwaveguides and respective output antennas, and any such number iscontemplated as falling within the scope of the present invention. Italso will be appreciated that other types of modulators may be employedalternative to the electro optic type modulator. For example, switchingdiodes may be used to alternately open or short-circuit short lengths ofwaveguide, thereby producing phase shifts in the passing microwaveradiation. Micromachined mechanical switches are also a suitablealternative, as they can be used in phase shift modulators atfrequencies above 10 gigabits per second.

FIG. 7 illustrates an optical signal transmitter 228 in accordance withanother embodiment of the present invention. The optical signaltransmitter 228 is essentially the same as the optical signaltransmitter 28 described in reference to FIGS. 3 and 4 except that theoptical signal transmitter 228 provides for frequency stabilization ofthe optical magnetron 52. In the Figures, like components are designatedby like reference numerals.

As is illustrated in FIG. 7, the optical signal transmitter 228 includesa mixer element 230. During operation of the optical signal transmitter228, the frequency or phase of the output radiation as detected from oneof the output horn antennas 218 is compared via the mixer element 230 toa reference frequency standard 242 to detect any undesirable instabilityor drifting in the output frequency or output phase. To correct suchdifferences in the frequency or phase, error voltages are applied to themodulation element 56 through a frequency control loop 246 and via thedata input terminals 210 and 212.

FIGS. 8 and 9 illustrate an optical signal transmitter 258 in accordancewith another embodiment of the present invention. The optical signaltransmitter 258 is essentially the same as the optical signaltransmitter 28 described in reference to FIGS. 3 and 4 except that theoptical signal transmitter 258 does not include an intra cavitymodulator element 56 but rather a plurality of extra-cavity modulatorelements 260. In the Figures, like components are designated by likereference numerals.

As is illustrated in FIGS. 8 and 9, each output waveguide 216 of theoptical signal transmitter 258 is provided with a high speed modulatorelement 260. More particularly, each output waveguide 216 has amodulator element 260 in line with the optical radiation path defined bythe output waveguide 216. For example, each modulator element 260 may bemade up of a window (not shown) of electro optic material such aslithium niobate with electrodes disposed along the sides of thematerial. In this regard, the modulator may be placed within a waveguideand modulated by electrodes which produce electric fields across thediameter of the waveguide. Data input terminals 270 and 272 areelectrically connected to the electrodes of each modulator element 260to supply a digital modulation signal thereto.

Independent data streams may be applied to each modulator element 260via the outgoing multiplexer 46 so that output radiation transmittedthrough one output waveguide 216 may be modulated in a mannerindependent of the output radiation transmitted through another outputwaveguide 216. Again, therefore, select programming may be delivered toeach of the respective neighborhood end users 22. One of ordinary skillin the art will appreciate that adjacent output antennas 218 of theoptical signal transmitter 258 may be cross polarized to avoidinterference between nearby optical beam transmissions.

It further will be appreciated that the independent modulator elements260 enable use of the entire frequency spectrum of the optical magnetron52 to each neighborhood end user 22. The data delivery rate to eachneighborhood end user 22 may thus be substantially increased. Forexample, for an optical signal transmitter 258 having up to about 10output antennas 218, the optical signal transmitter 258 transmits dataat a rate of up to about 50 gigabits per second from each output antenna218.

Also, in general, modulator elements are capable of operating at higherdata rates when they are placed in a single mode output waveguide suchas the optical waveguide 216 of the optical signal transmitter 258, thanwhen they are placed, for example, in the resonant cavity structure 102.In this regard, modulation rates can be up to about half the outputcarrier frequency. For example, for an output frequency of 250 Ghz, themodulation rate could be as high as about 100 gigabits per second ineach output waveguide 216.

As is well known to persons skilled in the art, for a given data linkdistance and size, increasing the data rate requires increased transmitpower in direct proportion to the data rate. Very high transmissionrates to large service areas, such as 100 gigabits per second to entireneighborhoods, requires relatively high power sources on the order ofabout hundreds of watts to kilowatts per output waveguide beam.Heretofore, sufficient power levels were not available at carrierfrequencies above 100 Ghz. Indeed, conventional optical data linkstypically use milliwatts in tightly focused beams, and can only providepoint-to-point service to a limited number of end users. The presentinvention addresses both the need for very high transmission rates andthe need for high output power.

FIG. 10 illustrates an optical signal transmitter 288 in accordance withyet another embodiment of the present invention. The optical signaltransmitter 288 is essentially the same as the optical signaltransmitter 258 described in reference to FIGS. 8 and 9 except that theoptical signal transmitter 288 provides for frequency stabilization ofthe optical magnetron 52. In the Figures, like components are designatedby like reference numerals.

As is illustrated in FIG. 10, the optical signal transmitter 288includes an intra-cavity modulator element 290, an extra-cavitymodulator element 292, and a mixer element 294. During operation of theoptical signal transmitter 288, the frequency or phase of the outputradiation as detected from one of the output horn antennas 296 iscompared via the mixer element 294 to a reference frequency standard 298to detect drifting in the output frequency or output phase. To correctsuch differences in the frequency or phase, error voltages are appliedto the modulation element 290 through a frequency control loop 302 andvia the data input terminals 304 and 306.

Referring now to FIG. 11, there is illustrated an optical signaltransmitter 308 in accordance with yet another embodiment of the presentinvention. The optical signal transmitter 308 is essentially the same asthe optical signal transmitter 28 described in reference to FIGS. 3 and4 except that the optical signal transmitter 308 includes anintra-cavity mode locking device 310 which produces repetitiveshort-duration pulses of radiation with very high peak power. In theFigures, like components are designated by like reference numerals.

In FIG. 11, L is the resonator length between the outer surface 98 ofthe anode 72 and the inner surface of the optical resonator 102. Thefrequency F of the allowed modes of the optical resonator 102 are givenapproximately by F=Nc/2L, where c is the speed of light and N is themode number. N is an integer which may range from one to severalthousands, and is approximately equal to the number of half-wavelengthsin the distance L for any particular operating wavelength. In general, amultiplicity of modes may oscillate simultaneously and independently. AsL is made longer, more modes become possible within a given frequencyinterval. The frequency spacing between allowed modes is givenapproximately by f=c/2L.

Short pulse operation occurs when the independent N modes are coupled(or “locked”) together. The optical magnetron 308 of the optical signaltransmitter 308 may be mode-locked by applying a periodic input voltageto the data input terminals 210 and 212 connected to the high speedmodulator element 56. When the period of the modulating voltage equalsthe period of the mode frequency spacing, locking occurs. In otherwords, mode locking occurs when the modulating frequency equals thefrequency spacing between modes, f=c/2L.

Turning now to FIGS. 12 a and 12 b, there is shown two types ofreceivers 320 and 322 in accordance with the present invention. Thereceiver 320 includes multiple input horn antennas 326 and a singlemixer element 328. The input horn antennas 326 receive opticalcommunication signals from the respective neighborhood end users 22, forexample. The mixer element 328 compares the frequency of the receivedsignal with a reference frequency and generates an information datasignal therefrom, for example a video or audio data signal. The datasignal may then be routed to the incoming demultiplexer and furtherprocessed, for example, in the manner earlier described. The receiver322 is similar to the receiver 320 except that there is a mixer element340 associated with each input horn antenna 342. Accordingly, the mixerelements 340 provide independent reference frequencies with whichoptical signals from the respective end users 22 may be compared beforeor as the signals are transmitted to the incoming demultiplexer.

It will be appreciated that the optical signal transmitter of thepresent invention is suitable for operating at frequencies heretoforenot possible with conventional microwave through-the-air transmitters.The optical signal transmitter of the present invention is capable ofproducing high efficiency, high power electromagnetic energy atfrequencies within the infrared and visible light bands, and which mayextend beyond into higher frequency bands such as ultraviolet, x-ray,etc.

Although the invention has been shown and described with respect tocertain illustrated embodiments, equivalent alterations andmodifications will occur to others skilled in the art upon reading andunderstanding this specification and the annexed drawings. In particularregard to the various functions performed by the above describedintegers (components, assemblies, devices, compositions, etc.), theterms (including a reference to a “means”) used to describe suchintegers are intended to correspond, unless otherwise indicated, to anyinteger which performs the specified function of the described integer(i.e., that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary embodiment or embodiments of the invention.In addition, while a particular feature of the invention may have beendescribed above with respect to only one of several illustratedembodiments, such feature may be combined with one or more otherfeatures of the other embodiments, as may be desired and advantageousfor any given or particular application.

The present invention includes all such equivalents and modifications,and is limited only by the scope of the following claims.

1. An optical communication system, comprising: an optical signalcommunication station for communicating optical signals to an end userspaced from the optical signal communication station; wherein theoptical signal communication station includes a high efficiency/highpower optical source which transmits high frequency opticalcommunication through the air to the end user, wherein the highefficiency/high power optical source includes a cathode an anode spacedfrom the cathode, an interaction space between the anode and thecathode, and a magnetic field source.
 2. The optical communicationsystem of claim 1, further including an end user, wherein the end userincludes an optical signal transmitter which transmits high frequencyoptical communications through the air to the optical signalcommunication station.
 3. The optical communication system of claim 1,wherein the high efficiency/high power optical source includes anoptical magnetron.
 4. The optical communication system of claim 1,wherein the high efficiency/high power optical source includes a phasedarray source of electromagnetic radiation.
 5. A method of communicatinghigh frequency optical signals through the air from an optical signalcommunication station to an end user, comprising: modulating aninformation signal with a high efficiency/high power optical source thatincludes a cathode, an anode spaced from the cathode, an interactionspace between the anode and the cathode, and a magnetic field source toobtain a high frequency optical signal; and transmitting the highfrequency optical signal through the air to the end user.
 6. An opticalcommunication system, comprising: a service provider which receivesinformation signals and converts the information signals into opticalsignals having a frequency in the broad bandwidth frequency range; anoptical fiber network which receives the optical signals from theservice provider; and a high efficiency/high power optical source whichreceives the optical signals from the optical fiber network andtransmits the optical signals through the air to an end user spaced fromthe high efficiency/high power optical source, the high efficiency/highpower optical source comprising at least one of an optical magnetron ora phased array source of electromagnetic radiation, the opticalmagnetron or phased array source including a cathode, an anode spacedfrom the cathode, an interaction space between the anode and thecathode, and a magnetic field source.
 7. The optical communicationsystem of claim 6, further including a receiver which transmitsinformation signals to the service provider. 8-9. (canceled)
 10. Anoptical communication system, comprising: an optical signalcommunication station including a first optical signal receiver and afirst high efficiency/high power optical source; one or more end usersspaced from the optical signal communication station, each end userincluding a second optical signal receiver and a second highefficiency/high power optical source; wherein the first highefficiency/high power optical source transmits through the air firstoptical signals having a frequency in the broad bandwidth frequencyrange and one or more of the second optical signal receivers of therespective end users detects the first optical signals, and the secondhigh efficiency/high power optical source transmits through the airsecond optical signals having a frequency in the broad bandwidthfrequency range and the first optical signal receiver of the opticalsignal communication station detects the second optical signals, thefirst high efficiency/high power optical source comprising at least oneof an optical magnetron or a phased array source of electromagneticradiation, the optical magnetron or phased array source including acathode, an anode spaced from the cathode, an interaction space betweenthe anode and the cathode, and a magnetic field source.
 11. The opticalcommunication system of claim 10, wherein the optical communicationsystem includes an optical signal communication tower.
 12. The opticalcommunication system of claim 10, wherein the first high efficiency/highpower optical source and the second high efficiency/high power opticalsource are substantially the same.
 13. The optical communication systemof claim 10, wherein the first high efficiency/high power optical sourceincludes an optical magnetron.
 14. The optical communication system ofclaim 10, wherein the first high efficiency/high power optical sourceincludes a phased array source of electromagnetic radiation. 15-35.(canceled)
 36. The optical communication system of claim 1, wherein theanode, cathode, and magnetic field source are coaxially aligned.
 37. Theoptical communication system of claim 3, wherein the optical magnetronincludes an optical resonator having a plurality of radially extendingoutput ports through which optical signals are transmitted.
 38. Theoptical communication system of claim 10, wherein the anode, cathode,and magnetic field source are coaxially aligned.
 39. The opticalcommunication system of claim 13, wherein the optical magnetron includesan optical resonator having a plurality of radially extending outputports through which optical signals are transmitted.